Fix boot failure when use secure boot supported (-D SECURE_BOOT_ENABLE=TRUE) OVMF packages

[wojiaohanliyang]

https://bugzilla.tianocore.org/show_bug.cgi?id=4807

This patch series provides fixes for using secure boot enabled OVMF packages when launch a VM.

The fixes include:

• Detect FlashNvVarStore before validate it in PlatformInitLib
• Init the whole EmuVariableNvStore before copy the content from FlashNvVarStore
• Mapping the address range of FlashNvVarStore correctly before access these region